In theory expensive,however if you get a good card which consumes very little electricity I would not say that it is expensive anymore because you win over the long run.For example if you can find the Rx 6600 at 50 watt in that hash rate I consider it a good investment but if you find Rx 580 at 130 watt then it is not a good investment over time.It all depends on your electricity price,the cards which run with very low power consumption are not a headache,ten cards at 50 watt each is 500 watt while ten cards at 130 watt each is 1300 watt in total and that is a big difference.